Another way to look at it
I agree with your basic conclusion about enterprise uptake, and many of the pros/cons of W8 you outlined in your piece.
My view is that over the last several release cycles MS is developing a release cadence with some similarities to Intel's tick/tock cadence. For MS "tick" is the high volume uptake cycle with features and enhancements that merely perfect/consolidate the advancements of the previous cycle. "Tock" is the cycle where major enhancements and UI changes occur. The uptake won't be as great as for the "tick" cycle, but MS has certain structural advantages deriving from its relationships with H/W OEMs such that it will still sell a substantial number of "tock" windows copies.
Using this way of looking at things, XP was a "tick" (consolidating the advancements in W2000 and the W95/98 line), Vista was a "tock", and W7 is a "tick". Hence, W8 will be a "tock" -- MS (in my view) does not expect major enterprise uptake with this release -- as you point out many are just commencing their migrations from XP to W7 (I would argue that timing and other considerations will mandate that going forward, enterprises will only adopt "tick" releases in any volume).
IMV many of the feature and UI constraints are best understood by what's going on underneath the covers. With W8 MS is starting to migrate all low-level developer interfaces from win32 to winrt. This effort will probably not be complete until the W9 timeframe. Business needs probably dictated that the initial version of winrt focus on the tablet and ARM support requirements. The downside to the partial migration in W8 is that MS must support both win32 and winrt, and it need to do this in a mostly sandboxed way (no hybrid win32/winrt apps allowed). This explains the existence of separate "Metro" and "Desktop" environments, and probably also the issues with Mozilla et al vis a vis browsers ("Desktop" on ARM is nothing at all like "Desktop" on x86).
My guess is that "Metro"/"Desktop" distinctions will disappear in the W9 timeframe as win32 fades from view.
